Even though water is abundantly available on the earth in the form of oceans, lakes, rivers etc., only a little portion is fit for drinking purposes. Hence, most of the rural population depends on the ground water. The poor quality of ground water makes the people to suffer due to different diseases. The problem of excessive fluorides in drinking water is a matter of serious concern around the world. Fluoride as low as 1 ppm (mg\L) causes breakdown of collagen, the most abundant of the body's protein at 30%. The concentration above 2 ppm gives permanent teeth a chalky-white appearance or the mottled brown-satin coloration to children less than 10 years of age. Fluoride above 4 ppm in drinking water can cause a condition of dense and brittle bones, known as osteoporosis, or marble bones called skeleton fluorosis. Fluoride replaces hydroxides in bones and thus is deposited in bones and causes chronic effect, known as skeleton fluorosis. The acceptable limits of fluoride ion in drinking water according to W.H.O. is 1.5 mg/litre of water. Hence it is utmost important to purify the water before its use by Adsorption technology for removal of fluoride ion from water is one of the commercially viable technology.
The present invention provides a process for the preparation of carbon supported activated alumina adsorbent useful for removal of fluoride ion from water.
An invention relating to a process in removing fluoride ion from waste water from silicon processing, through neutralization was disclosed in a U.S. Pat. No. 6,436,297. This invention highlights the method based on physicochemical processing for the removal of F− form water using milk of lime (Ca(OH)2 suspended in water) which is based on the spontaneous precipitation in the form of calcium fluoride (CaF2) of the fluoride ions in the presence of calcium ions following the equation:2F+Ca−++CaF2 
Reference may be made to another U.S. Pat. No. 2,059,553 discloses the removal of fluoride by adsorption process on the activated alumina in presence of alkali metals. The pH of the water is maintained at 4-8. Reference may be made to yet another U.S. Pat. No. 2,043,705 gave a comparative study of the adsorption properties of the hydroxides of aluminium, iron, zinc and manganese based on the precipitation method. Among all aluminium hydroxide is observed as the best. A publication by A. M. Raichur in separation and purification Technology (24 (2001) 121-127), explained about the removal of F− using rare earth oxides. Another publication by R. H. Mc kee in Industrial Engineering chemistry (26 (1934) 849) reveals the defluoridation by active carbon. Yet another reference may be made to a publication on defluoridation by R. Leyva Ramos, et al in Carbon (37 (1999) 609-619), which reports the use of Al impregnated on activated carbon using aluminum nitrate precursor. This catalyst adsorbs F− in acidic condition (i.e. pH-3).
The main limitations of the above mentioned patents and publications are:                1. Adsorption processes requires acidic conditions.        2. Addition of alkali metal ions for best adsorption.        3. In the precipitation method the separation of the pure water is a tedious process and there is no recovery of the catalyst.        
On the contrary, the present invention highlights the very simple way of making a highly efficient adsorbent for removal of fluoride ion without using alkali metal ions and easy way of operation i.e., in neutral pH-conditions.